Electromagnetic switch.



.l. L. WOODBRIDGE.

I ELECTROMAGNETIC SWITCH.

APPLICATION FILED FEB. 6, 1915.

1,225,388. Patented May 8,1917.

59,516 [eater M/ovdr/fig,

JOSEPH LESTER woomm'meE, or PHILADELPHIA, rENNsYLvAN A.

ELECTROMAGNETIC SWITCH.

Specification of Letters Patent.

Application filed February 6, 1915. Serial No. 6,413.

.To all whom z'tmay concern:

Be it known that I, J osnrrr LESTER WOOD- BRIDcE, a citizen of the United States, and a resident of Philadelphia, in the county of Philade1phia,'State of Pennsylvania, have invented certain new and useful Improvements in Electromagnetic Switches, of which the following is a specification.

My invention relates to switches which are operated by a coil responsive to the voltage across a given circuit, and one of the objects of my invention is to make the operation of such switches more accurate in 're-' sponse to said voltage. For this purpose I is employ a coil for controlling the operation of the switch, and in-series therewith ll connect a resistor having a marked negative temperature coefficient sufiicient to produce a drooping characteristic, that is a drop in ac voltage across the terminals of the resistor with increments of current within a certain range. The resistance'of the operating coil is so designed as to cooperate with the characteristics of the resistor to produce the re- 3 sults set forth below.

One embodiment of my invention will now be described in connection with the ac-.

companying. drawings, in which Figure 1 is a diagrammatic representation of apparatus and circuits involving features cit my invention, and Fig. 2 is a diagram showing I the relation of voltage and current in difierts of the control circuit of Fig. 1.

erring to-l ig. LA isa dynamo and F i coil, the dynamobeing connected to circuit 1, 2. Across this circuit is also a storagebattery B. in the conduster 2 is interposed an electromagnetic ewitch S-having two operating coils C and Uoil D is connected in sericslwith conductor'Q, while-coll G is connected in shunt across thecircuit 1, 2. Coil therefore, determines the closing of the switch in accordance with the-voltage across the circuit the dynamo to the battery passing through coil D will cause the latter to cooperate w th coil U to hold the switch 1n closed pol by a lowering of the voltage of mo and a discharge of the batterye coil-D to oppose coil G and when aloit' current reaches a suliicient switch will open. I round that me switch otthis Z. Afterfthe switch is closed current trom ion, while reversal of current in. the col Patented May 8, 1917.

character the magnetizing force required to close the switch is considerably greater than the value to which this magnetizing force must fall in orderto permit the switchto open. As a result of this, the dynamo voltage must rise to a value abnormally high 'in order to close the switch, or if the switch is designed to close at normal voltage a very consid- 'erable reversal of current in the coil D willbe necessary to open it, and as soon as the switch is opened the current in coil D being interrupted, the switch is liable to close again causing some chattering.

In the present invention these results are obviated by inserting a resistor R having a marked negative temperature coeiiicient in series with coil C. This negative tempera ture coeflicient should preferably be of sufiicient value to cause an actual drop in the voltage across the terminals of the resistor with increments of current within a certain range of current values. A suitable charac teristic for this resistor is shown hy the curve Y in Fig. 2 which represents the lation of voltage and current in the resistor. In-order to secure the best results the re sistance of coil. C should be adapted to the characteristic curve Y in such a manner that the characteristic of the two combined shall produce a characteristic curve similar to coil C should be as shown by the line X in Fig. 2. .Then the curve Z will be derived from. curves X and Y by adding the ordinates, as, for example, the ordinate PQ; of

. curve X added to the ordinate PM of curve Y produces the ordinate PN of curve Z.

The curves X and Y should be such that their combined characteristic curve Z starting from the-origin nearly vertically should turn abruptly when ya certain voltage is reached and becomenearly horizontal.

its a result of this combination, it will be seen that when the voltage across the circuit 1, 2 is below the critical value, only a very small amount of current; will flow through the 0011 C, but when the voltage to this critical value the 'currentin the will increase rapidly with very small increments of voltage. 1 -is will the s itch S to close very positively reversal of current in the coil i3.

esired voltage, and to open again. W1; little fall or voltage, and a very Having described my invention. what I claim and desire to secure b'yLetters Patent'isf 'In" an electromagnetic switch, the combination of a movable switch element, a coil adapted, upon energization, to operate said 'elementto close the switch, said coil having a rising voltage characteristic with increments of current therethrough, ancl in series with said coil a negative temperature coeflicient resistor of material characterized JOSEPH LESTER WOODBRIDGE.

' Witnesses:

R. A. WHrrsToNE, Jr.,

G. ROGERS. 

